<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body {
            min-width: 320px;
            max-width: 750px;
            background-color: pink;
            /* margin: 0 auto; */
        }
        /* .header {
            width: 600px;
            height: 1000px;
            background-color: pink;
            margin: 0 auto;
        }
        .fixed {
            position: fixed;
            top: 0;
            left: 50%;
            transform: translateX(-50%);
            width: 600px;
            height: 100px;
            background-color: greenyellow;
        } */
    </style>
</head>
<body>
    123
</body>
</html>